6. THE EXTRAGALACTIC BACKGROUND AND RELATED EXOTICA

The most commonly cited argument that the diffuse far ultraviolet
background is in part, or entirely, extragalactic is that this flux is
uniform over the celestial sphere, at least at high Galactic latitudes.
While it is now clear that the data supporting this
argument are deficient and most of the flux is due to
processes in the Galaxy, it is also clear that
some minimum flux (typically a few hundred CUs) is
present in all view directions at high Galactic latitudes.
Further, as summarized in Table 1,
the intensity of this flux is still finite when extrapolated to zero
neutral Galactic hydrogen column. It may well be that this flux is
uniform across the sky and the scatter in the data reported in
Table 1
only represents experimental uncertainty.
Even if this is true, however, it is by no means
established that this flux is extragalactic since it could be the
product of geocoronal, solar system, or Galactic effects. Indeed,
Hurwitz, Bowyer, and
Martin (1991) and
Martin, Hurwitz, and
Bowyer (1990)
have provided evidence discussed earlier in this review that the
majority of this ``uniform'' flux is
Galactic in origin.

Despite these uncertainties, it has been established that
the far ultraviolet background does convey information on a variety
of topics that might be classified as ``cosmological'' in
character. I review some of these topics in the following.